| As a catastrophic geological disaster,rock avalanche has been one of the hot issues in the field of engineering geology at home and abroad.This paper adopts field geological survey,low-altitude unmanned aerial vehicle photogrammetry(UAV)and indoor numerical simulation which is taking Nyixoi chongco rock avalanche(NCRA)as an example,aiming to discuss the various types of rheological accumulation landform(toreva blocks,longitudinal ridges,transverse ridges,levees,conjugate troughs,hummocks and megablocks),the vertical zonation characteristics caused by the instability of landslide and its geomophogensis.At last,the whole process of landslide from instability to stop accumulation is analyzed by numerical inversion with hydrodynamic software-Massflow.This paper mainly obtains the following three conclusions:(1)Through UAV photogrammetry and data post-processing,the areal high-resolution image data and high-precision digital elevation model(DEM)of NCRA are obtained.Based on Arc GIS,we extract the micro geomorphic characteristic factors(slope,aspect,roughness,relief)and the geometry size of surface landform and megablocks on the surface of accumulation zone,and reconstruct the topography and geomorphology before the sliding.According to the distribution characteristics of typical rheological accumulation landforms developed in the landslide area,the landslide area is divided into source area(I),translation zone(II)and accumulation zone(III-1,III-2,III-3 and III-4).Typical accumulation landform proves the change of the internal movement state of the sliding body,it shows the sliding body is extension-dominated sliding process in the translation zone(II),compression-dominated sliding process in subzones(III-1),compression and radial spreading-dominated sliding process in subzones(III-2,III-3),and rapid spreading-dominated sliding process in subzones(III-4);The megablocks is regularly changeable along the longitudinal section direction,and the bigger mageblocks are gathered in the middle landslide.It indicates that the fragmentation degree of rocks on the surface:translation zone(II)>accumulation zone(III-3,III-4)>accumulation zone(III-1,III-2),the fragmentation degree of block is related to the change of topography.(2)The sedimentary deformation facies of NCRA emerges the vertical zonation characteristics,different internal sedimentary structures developed in different layers.This facies can be divided into four layers from top to bottom:Carpace facies,Body facies,Basal facies and Substrate.The body facies can be further divided into four sub-facies:Blocky facies,Jigsaw-fractured facies,Fragmented facies and Inner sheared zone.Diapir structure and shear fracture zone are full in the body facies;Recumbent fold,flame structure,and basal décollements are found in the substrate position.The vertical zonation characteristics indicate that there is a strong shear-compression-fracture function between the sliding body and the substrate,and the formation reason is closely related to the suddenly change of topography fluctuation.(3)Based on ArcGIS and Massflow,we establish the numerical model of NCRA,The maximum accumulation thickness of the simulated source area is 130 m,Instable volume is2.8×10~7m~3.The numerical result shows:when choose the Coumlomb model and the friction coefficient?=0.16,The simulation results are close to the actual situation,and the coincidence rate T is 0.92.In the process of landslide instability,the maximum velocity is98m/s,the maximum accumulation thickness on the longitudinal section is 37.0 m,it's close to the measured value of 38.7 m,the area of simulated accumulation area is 3.77 km~2,the maximum horizontal moving distance 4.45 km,and they are slightly less than the actual measurement.The total movement time of sliding body is 128 s,and it can be divided into four stage:stage of start acceleration(0?20 s),stage of fast forward movement(20?66 s),stage of the front edge shifts down and stop accumulating(66?92 s),stage of trailing edge stop accumulating(92?128 s). |
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